Rheostat.



PATENTBD APR. 28, 1908. G. P. PACKARD.

RHEOSTAT.

APPLICATION FILED APR. 28,1906.

2 SHEETS-SHEBT 1.

WITNESSES: INVENTOR I v ATTORNEY No. 885,782. PATENTED APR. 28, 1908.

.G. F. PACKARD.

RHEOSTAT.

APPLICATION FILED APR. 28, 1906.

2 SHBBTS-SHEET 2.

WITNESSES? iNgHOR ATTORNEY UNITED STACEES PATENT OFFICE.

GRANVILLE F. PACKARD, OF PITTSBURG, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

RHEOSTAT.

Specification of Letters Patent,

Patented April 28, 1908.

Application flied April 28, 1906. Serial No. 314,275.

To all whom it may concern:

Be it known that I, GRANVILLE F. PACK- ARD, a citizen of the United States, and a resident of Pittsburg, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Rheostats, of which the following is a specification.

M invention relates to rheostats and it has fbr its object to provide a rheostat whereby any desired resistance between the limits of the device may be obtained.

Rheostats which have heretofore been provided for the purpose of adjusting the re sistances in the circuits of the shunt field magnet windings of electric motors have usually comprised sub divided resistanceelements and switch arms or other means for making circuit connections to the points of sub-division thereof. When so constructed, the resistances in the field circuits have of necessity been varied in ste s or radations and consequently the spec s of t e motors have also been varied in steps. .When motors are employed in the 0 eration of machine tools it is often essentia or at least very desirable, that they may be caused to operate at definite speeds that may correspond to resistance values between the steps of the rheostats. According to the present invention, I propose to provide the ordinary rheostats having sub-divided resistance elements with another resistance element the resistance of 'which is approximately equal to that between the points of sub-division of the other element andto which continuous circuit. connection may be made.

Figure 1 of the accompanying drawings is a face view of a rheostat constructed in accordance with my invention and Fig. 2 is a similar view of a modification of the vice of Fig. 1.

In F' l a resistance element 1 is sub divided y means of a set of annularly-arranged contact terminals 2 that are connected thereto at intervals with which a ivoted switch arm 3 is adapted'to engage in the usual manner. Arranged concentrically with and within the set of contact terminals 2 is a resistance strip or element 4 with which a shorter switch arm 5 is adapted to engage, the switch arm 5 bei concentrically with and being dfiactrically connected to the switch arm 3. A composition which has been found suitable for the pivoted resistance strip 4 comprises graphitoidal silicon, silicon oxld, lIOIl and a uminum in appropriate and varying proportions, such a the switch arm 3 until the speed of the motor is approximately that desired.v Then," in order to obtain exactl any desired or predetermined speed whic 1 it may be impossible to obtain by the adjustment of the switch arm 3, more or less of the resistance element 4 may be included in circuit by operation of the switch arm 5.

In Fig. 2 I have shown a rheostat in which is employed a resistance strip 8 of greater length and which may, consequently, be either of greater cross-sectional area or of less specific resistance than that of Fig. 1,

the greater length of the resistance strip being obtained by doubling it and placing it outside of and concentrically with an annularly-arranged set of contact terminals 9. Concentrically pivoted switch arms 10 and 11, that are insulated from each other, are adapted to en age, respectively, with the contact termina s and with both ortions of the doubled resistance strip. he switch arm 10 is connected to one end of the resist ance strip, the other end of which is connected to a binding post 12 or circuit terminal of the rheostat. e

In operation of the rheostat the current enters at binding 0st 13,- traverses subdivided rheostat cement 14, switch arm 10, the inner portion of the resistance strip 8, switch arm 11 and the outer portion of the resistance strip 8. Y

The structural details and arran ements of the parts may obviously be variet within considerable limits from what has here been shown and described without altering the mode, of-operation of the invention or departing material] from its spirit, and I therefore desire tiiat all such modifications be included within its scope.

I claim as my invention:

1. In a rheostat, the combination with a sub-divided resistance element and means for makin circuit connections to the points of sub-division thereof, of another resistance element and means for making continuous circuit connection thereto.

2. In a rheostat, the combination with a sub-divided resistance element and means for making circuit connections to the points of sub-division thereof, of another resistance element the resistance of which is approximately equal to that between the points of sub-division of the other element and means for making continuous circuit connection thereto.

In a rheostat, the combination with means for varying the resistance in steps or gradations, of means for varying the resistance uninterruptedly.

4. In a rheostat, the combination with means for varying the resistance in steps or gradations, of means for varying the resistance uninterruptedly between the steps or gradations.

5. A rheostat comprising two resistance elements, means whereby circuit connection may be made to one of them at intervals and meansfor making continuous circuit connection to the other.

6. In a rheostat, the'comhination with a set of annularly arranged contact terminals and a resistance strip arranged concentrically therewith, of switch arms that are concentrically pivoted and are adapted, respectively, to engage the contact terminals and the resistance strip.

7. In a rheostat, the combination with a set of annularly arranged contact terminals and a resistance strip arranged concentrically therewith, of switch arms that are concentrically pivoted and are adapted, respectively, to engage the contact terminals and the resistance strip, and means for making external circuit connections, respectively, to one of the contact terminals and to the resistance strip.

8. In a rheostat, the combination with a sub-divided resistance element and another resistance element, of means whereb Y the elements may be connected in series re ation and whereb connection may be made to the points of su -division of the one element and continuouslv to the other element.

9. In a rheostat, the combination with a set of contact terminals and a switch arm to engage therewith, of a doubled resistance strip and means for making continuous circuit connection to both portions thereof.

10. In a rheostat, the combination with a sub-divided resistance element and means for making circuit connection to the points of sub-division thereof, of a doubled resistance strip and means for making continuous circuit connection to both portions thereof.

11. In a rheostat, the combination with an annularly arranged set of contact terminals and a doubled resistance strip that .is arranged concentrically therewith, of switch arms that are concentrically pivoted and that are adapted, respectively, to engage the contact terminals and both portions of the resistance strip.

In testimony whereof, I have hereunto subscribed my name this 21st day of April, 1906.

GRANVILLE F. PACKARD.

Witnesses:

VERYL B. BROUGHTON, BIRNEY Hmns. 

